The alerting effects of caffeine, bright light and face washing after a short daytime nap.
Level 2 - randomized trial
Small controlled crossover trial in healthy volunteers
PubMed 14652086 · doi:10.1016/s1388-2457(03)00255-4
What was done
Ten young healthy adults participated in five daytime conditions tested around 12:40 PM: a 20-minute nap alone (Nap only); 200 mg caffeine followed by a 20-minute nap (Caffeine+Nap); a 20-minute nap followed immediately by 1 minute of 2,000 lx bright light (Nap+Bright-light); a 20-minute nap followed immediately by face washing (Nap+Face-washing); and rest without sleep (No-Nap). Participants completed computer tasks for 15 minutes before napping and for 1 hour after napping.
What was found
The abstract does not report numerical data, effect sizes, or p-values. Caffeine+Nap was reported as the most effective condition for subjective sleepiness and performance level, lasting throughout the 1-hour post-nap testing window. Nap+Bright-light was comparable to Caffeine+Nap for subjective sleepiness but not for performance. Nap+Face-washing showed mild and transient suppression of subjective sleepiness immediately after napping.
Why it matters
This study indicates that combining a short daytime nap with pre-nap caffeine or post-nap bright light exposure reduces mid-afternoon sleepiness more effectively than napping alone.
Limits
The sample size is very small (n = 10), and the abstract provides no quantitative data or statistical metrics. Blinding was not possible for interventions such as face washing or bright light, and follow-up was limited to one hour.
Cited by
- supports Taking a 25-minute nap immediately after drinking black coffee allows sleep to clear brain adenosine while caffeine binds to the receptor, providing boosted alertness for 4 hours.